Conventionally, a joint device for a robot includes a first arm having a window on a side surface of a frame, and a second arm fixed to a flange disposed inside the first arm. A worker inserts a bolt into the first arm through the window to fix a frame of the second arm to the flange by the bolt (e.g. Patent Document 1: JP 2002-239966 A).
In Patent Document 1, the fixed position of the bolt is adjacent to the center of the frame of the first arm. Hence, workability in assembling of the joint device through the window on the side surface of the frame may be low.